Wikipedia:Primary Secondary and Tertiary Sources

For information regarding classification of source material, with examples regarding the appropriate use or misuse of these sources in Wikipedia, see WP:PSTS.

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Proposed policy change to WP:NOR

Primary, secondary, and tertiary sources

All articles should rely on reliable, third-party published sources with a reputation for fact-checking and accuracy.^WP:Sources Though we may report the attributed opinions of reliable authors, articles should never include the opinions of Wikipedians themselves, even if you are an expert who has read any number of primary, secondary, or tertiary sources.

Your opinions and interpretations do not belong in an article. But it is appropriate to document interpretations of events, data, or opinions, as published in reliable secondary source material. Peer-reviewed sources are especially valued. While secondary source material is most preferred, primary sources may also be used to report factual material provided the contributing editor states the fact in a manner that does not present an interpretation of the fact (original research) which is not itself explicitly contained in the primary source.

The question of whether source material is secondary or primary should not, however, become a focal point for edit warring. Proper classification of sources can be complex because different definitions apply in different fields of knowledge. In addition, a single source may contain both primary and secondary material. For example, a peer-reviewed science article including original findings may include a scatter plot of data points and a cross-sectional x-ray (primary material), but it may also include valuable secondary material, such as the research team's synthesis and interpretation of prior published studies reviewed in the discussion of the results or as background for why the study was conducted.

Similarly, a 1863 newspaper about the Gettysburg Address may include secondary source quotes from text of the Address (the primary source being Lincoln's manuscript), but it would be a primary source of any commentary or observations about the Address. It might also include tertiary material if the reporter included a summary of written reports that appeared in other newspaper accounts.

The classification of a source may also vary depending on use. The same 1863 newspaper articles about Lincoln's speech become primary sources when used by a modern scholar to write a dissertation on media treatment and public reactions to Lincoln and the Civil War.

Because of these many variables, there is a grave risk that arguments about how a source should be classified can become occasions for unproductive edit warring and wikilawyering.

It is therefore important to remember that, according to policy, primary, secondary, and tertiary sources may all be acceptable if used appropriately. Therefore, how material is classified is far less important than making certain that the material cited from the source is accurately described without inserting interpretations which are not specifically present in the cited source. That is the essence of the "No Original Research" policy.

For additional information regarding classification of source material, with examples regarding the appropriate use or misuse of these sources in Wikipedia, please see Primary Secondary and Tertiary Sources.

NOTE: The following section would not be included in NOR policy. It would be a separate page offering guidelines.

Start of guidelines regarding use of primary, secondary and tertiary sources

According to Wikipedia's verifiability policy, any material that is challenged or likely to be challenged must be accompanied by a reliable source. In general, the most reliable sources are (a) peer-reviewed journals and books published in university presses, followed by (b) university-level textbooks; then by (c) magazines, journals, and books published by respected publishing houses; then by (d) mainstream newspapers.

Research that consists of collecting and organizing material from existing sources is encouraged: this is "source-based research," and it is fundamental to writing an encyclopedia. Problems often arise, however, when editors use sources in ways that constitute original research, or which violate Wikipedia's policy of neutrality.

This guideline sets factors that an editor should keep in mind while using various types of sources for verifying the statements in an article. Sources can be classified in various ways. The most useful classification is by their primary, secondary or tertiary in nature. Another classification is in terms of first-party or second-party.

Primary, secondary, and tertiary sources may all be appropriately used, if (1) they are used without engaging in original research or synthesis and (2) if in the event of conflicts between sources they are treated with the appropriate deference to the "better" source. These guidelines address these two principles.

The classification of primary, secondary, and tertiary sources can be different in various disciplines and may depend on the context in which the source is used. The examples and definitions given in these guidelines are provided as an aid for more informed discussion of these classification issues when they come up.

Definitions of primary, secondary and tertiary

Various professional fields treat the distinction between primary and secondary sources in differing fashions. Some fields and references also further distinguish between secondary and tertiary sources. Primary, secondary and tertiary sources are broadly defined here as follows:

Primary sources are sources very close to the origin of a particular topic or event. An eyewitness account of a traffic accident is an example of a primary source. Other examples include archeological artifacts; photographs; videos; historical documents such as diaries, census results, maps, or transcripts of surveillance, public hearings, trials, or interviews; untabulated results of surveys or questionnaires; the original written or recorded notes of laboratory and field research, experiments or observations which have not been published in a peer reviewed source; original philosophical works, religious scripture, administrative documents, patents, and artistic and fictional works such as poems, scripts, screenplays, novels, motion pictures, videos, and television programs.^[1]
Secondary sources are accounts at least one step removed from an event or body of primary-source material and may include an interpretation, analysis, or synthetic claims about the subject.^[2] Secondary sources may draw on primary sources and other secondary sources to create a general overview; or to make analytic or synthetic claims.^[3]^[4]
Tertiary sources are publications such as encyclopedias or other compendia that sum up secondary and primary sources. For example, Wikipedia itself is a tertiary source. Many introductory textbooks may also be considered tertiary to the extent that they sum up multiple primary and secondary sources.

Examples of Overlap of Primary and Secondary Material in a Single Source

The same source may contain both primary and secondary material, so if this becomes an issue, it is important to be able to understand the differences.

For example, a peer-reviewed medical journal article typically has four major parts. An introduction, a description of the methods used for the study, the results of the study, and a conclusion. Generally, the introduction includes a review of the prior published research relevant to the study. This portion of the article is therefore a secondary source offering a synthesis of the literature. The sections on the methods and results of the experiment may include both raw primary-source data (such as photographs and scatter plots of data points) plus analysis and synthesis of primary-source data collected in the experiment which is one step removed from the primary source material collected by the researchers. Finally, the conclusions section always offers a peer-reviewed synthesis of the findings, generally in the context of previously published studies.

Similarly, a newspaper article reporting what a scientist says at a press conference is a great secondary source documenting what a scientist stated. The same article providing a summary of what "most scientists believe" or what "most research shows" is reflecting a tertiary view, expressing the view of a reporter with limited expertise who has most probably looked at only a few sources and spoken to a few scientists.

A New York Times opinion piece may include secondary-source material, quoting from a government report, and primary-source material, the columnist's opinions regarding what the report means for the economy. The opinion piece itself is a primary source regarding the columnist's opinion, but a secondary source regarding predictions for the economy.

If the secondary source makes new, original insights or correlations, those new synthetic insights might be considered primary with respect to the new synthetic conclusions, and secondary with respect to the prior material.

Primary versus secondary sources may also vary depending on the expertise and access of the individual. For most people, government census reports are treated as a primary source. But to a historian, the primary data from a census are the questionnaires or the primary recordings of the survey data in registers, or the equivalents, and the census report itself is a secondary source reflecting the published analysis, synthesis and reporting of the census by experts.

These examples demonstrate why primary, secondary, and tertiary source definitions can be difficult for some editors to grasp, and a source for contention. While it is useful to grasp these distinctions, it is most important to just keep focused on using these sources in a manner which does not involve original research. Stick close to the facts and read the examples given in WP: SYNTH to avoid going beyond reporting the facts and opinions which appear in the sources you want to use. mc r

Use of peer-reviewed sources

Peer-reviewed articles are generally highly preferred sources because the process of peer review by experts in the field helps to assure that the facts and opinions in the article, while not necessarily true, are at least reasonable within the field. Generally, any respected journal will be indexed by the major indexing services for academic journals. A journal that is not indexed may be of questionable value.

Always remember to attribute opinions to the authors, not the publication. The conclusions of a scientist summarizing her team's findings in light of previous studies should be attributed to the lead author, not to the New England Journal of Medicine, for example.

Regardless of the classification, avoid original research

The key skill which must be employed to appropriately use any source, whether primary, secondary, or tertiary, is the ability to recognize the difference between a fact and an opinion and to always attribute opinions to the person providing it.

Facts: The most authoritative source for a fact is a primary source, but the most convenient source may be secondary or tertiary source.

Opinions, including a notable or authoritative interpretation of events, data, can only be drawn from a reliable secondary source which documents that it is a fact that some person holds that opinion or has synthesized a body of information in a fashion described in the Wikipedia article and cited to that source.

Tertiary sources are acceptable sources for general facts which are not controversial.

All interpretive claims, analyzes, or synthetic claims about primary sources which appear in Wikipedia articles should be referenced to a secondary source to avoid original analysis of the primary-source material by Wikipedia editors.

Primary sources that have been published by a reliable source may be used in Wikipedia, but only with care, because it is easy to misuse them. For that reason, anyone without specialist knowledge who reads the primary source should be able to verify that the Wikipedia passage agrees with the primary source. Any interpretation of primary-source material requires a reliable secondary source for that interpretation. To the extent that part of an article relies on a primary source, it should:

only make descriptive claims about the information found in the primary source, the accuracy and applicability of which is easily verifiable by any reasonable, educated person without specialist knowledge, and
make no analytic, synthetic, interpretive, explanatory, or evaluative claims about the information found in the primary source.

Unsourced material obtained from a Wikipedian's personal experience, such as an unpublished eyewitness account, should not be added to articles. It would violate both this policy and Verifiability, and would cause Wikipedia to become a primary source for that material.

Tertiary sources can be helpful in providing broad summaries of topics that involve many primary and secondary sources. Some tertiary sources may be more reliable than others, and within any given tertiary source, some articles may be more reliable than others. WP:Verifiability#Reliable sources describes some criteria for assessing the reliability of sources.

Appropriate sourcing can be a complicated issue, and these are general rules. Deciding whether primary or secondary sources are more suitable on any given occasion is a matter of common sense and good editorial judgment, and should be discussed on article talk pages.

It is strongly recommended that you read and understand the important distinction in reporting facts without inserting your own synthesis of facts as illustrated in the example of Smith and Jones found in WP:SYNTH.

Appropriate use of primary and tertiary sources

Primary sources are appropriate when the purpose of using them is purely illustrative, such as providing a photograph of a historic event in an article about that event or providing a quote of an author's prose in an article about the author. When using primary sources it is necessary to avoid attempts at interpreting the sources: the purpose is to give readers representative and neutral examples. Primary sources may also be used as references for specific uncontroversial facts that require no interpretation, such as names and dates.

Certain types of tertiary sources are useful on a supplemental basis. Basic reference works such as reputable encyclopedias are preferable to no citation at all, although reliable secondary sources should supplant those general reference works as the article improves. Articles of very high quality (good article and featured article) may use specialized tertiary sources on a supplemental basis to report high-level analysis that has occurred among experts in the field. Articles about science may source information about paradigm shifts to tertiary analyses; articles about history may source historiography and metahistory to tertiary studies, etc. For example, Christopher Columbus has been held in very high or very low esteem during different eras. So tertiary studies of Columbus's reputation would be appropriate citations for that section of the Columbus biography.

Tips on Avoiding Unnecessary and Unproductive Conflict

In non-controversial articles, some minor case of interpretation may not raise objections. For example, perhaps no one would object if in referencing a table of the heights of American presidents you wrote that "Only Abraham Lincoln was taller than Lyndon B. Johnson." But if your reference is a table of heights alone, such a statement of who is "taller" is actually an interpretation of fact. So if other editors object, which is their right to do, don't fight about how it is obviously true given the facts. Instead it is almost always best to just remove the interpretation and replace the bare bone facts, leaving the interpretation of the data to the reader. "Abraham Lincoln was 6 ft 4 in. Lyndon B. Johnson was 6 ft 3½ in." (By the way, do not cite a Wikipedia article, as we have done in this example.)

Another important technique to avoid conflict is to always reference the author of the source as expressing the opinion. "According to Dr. Ted Johnson, the invasion of nomadic tribes led to the fall of the Roman Empire"¹ is better than just "The invasion of nomadic tribes led to the fall of the Roman Empire." If challenged, it is even better to quote the authority, "According to Dr. Ted Johnson: 'It was the pressure of Germanic tribes crossing the Rhine and Danube which ultimately caused the disintegration of Rome's economic power."¹ Brief quotes are allowed under copyright law. So quoting an authority, and citing the authority not just in the footnote but in the text, is a good way to avoid accusations that you are engaging in original research. On the reverse side, please don't demand anything more than this from other editors who meet their obligation of providing a reliable source and summarize it accurately. Respect their contributions, even if you don't like the point of view reflected by their contributions.